1. Field of the Invention
The present invention relates to a dual spin-valve type magnetoresistive thin film element in which electrical resistance changes in response to the relationship between the magnetization direction of pinned magnetic layers and the magnetization direction of a free magnetic layer that is influenced by an external magnetic field. More particularly, the invention relates to a spin-valve type magnetoresistive thin film element in which satisfactory asymmetry can be obtained while maintaining a high rate of resistance variation, and to a spin-valve type magnetoresistive thin film head using the same.
2. Description of the Related Art
A spin-valve type magnetoresistive thin film element is a kind of giant magnetoresistive (GMR) element which uses a giant magnetoresistance effect, in which a high rate of resistance variation can be obtained in a relatively simple structure. Among spin-valve type magnetoresistive thin film elements, a single spin-valve type magnetoresistive thin film element has the simplest film structure, which includes 4 layers consisting of an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically-conductive layer, and a free magnetic layer. A dual spin-valve type magnetoresistive thin film element has a film structure in which a higher rate of resistance variation can be obtained in comparison with the single spin-valve type magnetoresistive thin film element.
FIG. 10 is a sectional view of a conventional dual spin-valve type magnetoresistive thin film element, taken from the surface facing a recording medium.
As shown in FIG. 10, on either surface of a free magnetic layer 1, a nonmagnetic electrically-conductive layer 2, a pinned magnetic layer 3, and an antiferromagnetic layer 4 are deposited in that order symmetrically, and on either side of the laminate, a hard magnetic bias layer 5 and a lead layer 8 are formed. Numeral 6 represents an under layer composed of a metal, such as Ta, and numeral 7 represents a protective layer composed of Ta or the like.
As shown in FIG. 10, the pinned magnetic layers 3 and 3 are formed in contact with the antiferromagnetic layers 4 and 4, and the magnetizations of the pinned magnetic layers 3 and 3 are fixed in the Y direction (depth direction) by exchange coupling magnetic fields generated at interfaces between the pinned magnetic layers 3 and 3 and the antiferromagnetic layers 4 and 4.
The hard magnetic bias layers 5 and 5 are magnetized in the X direction in the drawing (track width direction), and the magnetization of the free magnetic layer 1 is set in the X direction under the influence of biasing magnetic fields from the hard magnetic bias layers 5 and 5.
In the dual spin-valve type magnetoresistive thin film element, a sensing electric current is applied in the X direction from the lead layer 8 to the free magnetic layer 1, nonmagnetic electrically-conductive layers 2 and 2, and pinned magnetic layers 3 and 3. A magnetic recording medium such as a hard disk moves in the Z direction, and when a fringing magnetic field from the recording medium is applied in the Y direction, the magnetization of the free magnetic layer 1 changes from being in the X direction to being in the Y direction. There is a change in electrical resistance in response to the relationship between the change in the magnetization direction of the free magnetic layer 1 and the fixed magnetization direction of the pinned magnetic layers 3 and 3, and thus, the fringing magnetic field is detected.
In the conventional dual spin-valve type magnetoresistive thin film element, as shown in FIG. 10, the nonmagnetic electrically-conductive layers 2 and 2 which are formed on upper and lower surfaces of the free magnetic layer 1, respectively, have the same thickness h1, the pinned magnetic layers 3 and 3 are formed at the same thickness h2, and the antiferromagnetic layers 4 and 4 are also formed at the same thickness h3. That is, the conventional dual spin-valve type magnetoresistive thin film element has a structure in which laminates sandwiching the free magnetic layer 1 are perfectly symmetrical.
However, in the dual spin-valve type magnetoresistive thin film element having a vertically symmetrical structure, the magnetization direction of the free magnetic layer 1 is not stabilized, and it is very difficult to obtain satisfactory asymmetry (vertical asymmetry of the regenerated output waveform).
FIG. 11 is a longitudinal sectional view which schematically shows a spin-valve type magnetoresistive thin film head, including the dual spin-valve type magnetoresistive thin film element shown in FIG. 10, and a pair of shield layers. A sensing electric current 9 from the lead layer 8 flows perpendicularly with respect to the drawing toward the front.
As shown in FIG. 11, various magnetic fields are applied to the free magnetic layer 1. First, interlayer coupling magnetic fields Hbf1 and Hbf2 (interlayer exchange coupling+topological coupling) occur between the pinned magnetic layers 3 and 3, which are magnetized in the right direction in the drawing (direction perpendicular to a recording medium D; depth direction), and the nonmagnetic electrically-conductive layers 2 and 2, and the magnetic fields Hbf1 and Hbf2 influence the free magnetic layer 1 at the interfaces with the free magnetic layer 1.
Static magnetic coupling fields (demagnetizing fields) Hd1 and Hd2 are also applied into the free magnetic layer 1 from the pinned magnetic layers 3 and 3.
The sensing electric current 9 mainly flows through the nonmagnetic electrically-conductive layers 2 and 2 having low resistivity, and induction magnetic fields Is1 and Is2 by the sensing electric current 9 influence the free magnetic layer 1.
Additionally, as shown in FIG. 11, a lower shield layer 10 is formed on the lower side of the spin-valve type magnetoresistive thin film element at a distance GL1 from the center of the free magnetic layer 1 of the spin-valve type magnetoresistive thin film element. An upper shield layer 11 is formed on the upper side of the spin-valve type magnetoresistive thin film element at a distance GL2 from the center of the free magnetic layer 1. Under the influence of the induction magnetic fields by the sensing electric current 9, shield bias magnetic fields occur from the lower shield layer 10 and the upper shield layer 11. A shield bias magnetic field S1 from the lower shield layer 10 and a shield bias magnetic field S2 from the upper shield layer 11 influence the free magnetic layer 1.
Herein, when magnetic fields applied to the free magnetic layer 1 in the right direction in the drawing, that is, interlayer coupling magnetic fields Hbf1 and Hbf2, the induction magnetic field Is2, and the shield bias magnetic field S2, are assumed to have positive values and when magnetic fields applied to the free magnetic layer 1 in the left direction in the drawing, that is, static magnetic coupling fields Hd1 and Hd2, the induction magnetic field Is1, and the shield bias magnetic field S1, are assumed to have negative values, if the sum of all the magnetic field values applied to the free magnetic layer 1 is zero, magnetic fields affecting the free magnetic layer 1 are totally offset, enabling satisfactory vertical asymmetry of the regenerated output waveform, which is so-called xe2x80x9casymmetryxe2x80x9d.
In the conventional spin-valve type magnetoresistive thin film element, as described above, since laminates disposed on the upper and lower surfaces of the free magnetic layer 1 are perfectly symmetrical, the induction magnetic field Is1 flowing from the lower laminate into the free magnetic layer 1, and the induction magnetic field Is2 flowing from the upper laminates into the free magnetic layer 1, have the same intensity, and as shown in FIG. 11, since induction magnetic fields Is1 and Is2 flow into the free magnetic layer 1 in opposite directions, the magnetic fields Is1 and Is2 are offset with respect to each other.
Next, since the distance GL1 from the center of the free magnetic layer 1 to the lower shield layer 10 and the distance GL2 from the center of the free magnetic layer 1 to the upper shield layer 11 are the same, the shield bias magnetic field S1 from the lower shield layer 10 applied to the free magnetic layer 1 has the same intensity as that of the shield bias magnetic field S2 from the upper shield layer 11 applied to the free magnetic layer 1. Since shield bias magnetic fields S1 and S2 flow in directions opposite to each other, the magnetic fields S1 and S2 are also offset with respect to each other.
That is, in order to adjust the vector sum of all magnetic fields entering into the free magnetic layer 1 to zero, in the spin-valve type magnetoresistive thin film element shown in FIG. 11, the vector sum of magnetic fields excluding the induction magnetic fields Is1 and Is2 and the shield bias magnetic fields S1 and S2, that is, Hbf1+Hbf2+Hd1+Hd2, must be adjusted to zero.
However, it is very difficult to adjust the vector sum of Hbf1+Hbf2+Hd1+Hd2 to zero under the conditions that upper and lower nonmagnetic electrically-conductive layers 2 and 2 have the same thickness h1, and upper and lower pinned magnetic layers 3 and 3 have the same thickness h2 as shown in FIG. 10.
Even if the vector sum of Hbf1+Hbf2+Hd1+Hd2 can be adjusted to zero by selecting the thicknesses h1 and h2 while maintaining the same thickness h1 for the nonmagnetic electrically-conductive layers 2 and 2 and the same thickness h2 for the pinned magnetic layers 3 and 3, although satisfactory asymmetry may be obtained, the rate of resistance variation is decreased instead, and thus characteristics of dual spin-valve type magnetoresistive thin film elements, in which a higher rate of resistance variation can be obtained in comparison with single spin-valve type magnetoresistive thin film elements, cannot be displayed.
The present invention overcomes the difficulties noted above with respect to the related art. It is an object of the present invention to provide a spin-valve type magnetoresistive thin film element in which satisfactory asymmetry can be obtained while maintaining a higher rate of resistance variation than that in a single spin-valve type magnetoresistive thin film element, and to provide a spin-valve type magnetoresistive thin film head using the same.
A spin-valve type magnetoresistive thin film head in accordance with the present invention is provided with a spin-valve type magnetoresistive thin film element which includes a free magnetic layer; an upper nonmagnetic electrically-conductive layer and a lower nonmagnetic electrically-conductive layer sandwiching the free magnetic layer; an upper pinned magnetic layer and a lower pinned magnetic layer formed on the upper and lower nonmagnetic electrically-conductive layers, respectively, the magnetization directions of the upper and lower pinned magnetic layers being fixed; and an upper antiferromagnetic layer and a lower antiferromagnetic layer formed on the upper and lower pinned magnetic layers, respectively; in which a sensing electric current is applied in the direction perpendicular to the fixed magnetization of the pinned magnetic layers, and electrical resistance changes in response to the relationship between the fixed magnetization of the pinned magnetic layers and the variable magnetization of the free magnetic layer. The vector sum of Hbf1+Hbf2+Hd1+Hd2+Is1+Is2+S1+S2 is zero, where the intensity of the magnetic field caused by interlayer coupling between the lower pinned magnetic layer and the lower nonmagnetic electrically-conductive layer is represented by Hbf1 (vector), the intensity of the magnetic field caused by interlayer coupling between the upper pinned magnetic layer and the upper nonmagnetic electrically-conductive layer is represented by Hbf2 (vector), the intensity of the static magnetic coupling field applied from the lower pinned magnetic layer to the free magnetic layer is represented by Hd1 (vector), the intensity of the static magnetic coupling field applied from the upper pinned magnetic layer to the free magnetic layer is represented by Hd2 (vector), the intensity of the induction magnetic field by an electric current applied to the free magnetic layer from the lower side is represented by Is1 (vector), the intensity of the induction magnetic field by an electric current applied to the free magnetic layer from the upper side is represented by Is2 (vector), the intensity of the shield bias magnetic field applied to the free magnetic layer from a lower shield layer formed on the lower side of the spin-valve type magnetoresistive thin film element with a gap layer therebetween is represented by S1 (vector), and the intensity of the shield bias magnetic field applied to the free magnetic layer from an upper shield layer formed on the upper side of the spin-valve type magnetoresistive thin film element with a gap layer therebetween is represented by S2 (vector).
In the present invention, the vector sum of Hbf1+Hbf2+Hd1+Hd2+Is1+Is2+S1+S2 may be adjusted to zero by creating a difference in thickness between the upper and lower nonmagnetic electrically-conductive layers and by changing the amount of the sensing electric current and the direction of the sensing electric current.
In such a case, preferably, the lower nonmagnetic electrically-conductive layer has a thickness of 16 to 38 angstroms and the upper nonmagnetic electrically-conductive layer has a thickness of 19 to 38 angstroms.
In the present invention, the vector sum of Hbf1+Hbf2+Hd1+Hd2+Is1+Is2+S1+S2 may be adjusted to zero by creating a difference in thickness between the upper and lower pinned magnetic layers and by changing the amount of the sensing electric current and the direction of the sensing electric current.
In such a case, preferably, the upper and lower pinned magnetic layers have a thickness of 15 to 80 angstroms.
In the present invention, the vector sum of Hbf1+Hbf2+Hd1+Hd2+Is1+Is2+S1+S2 may be adjusted to zero by creating a difference in thickness between the upper and lower antiferromagnetic layers and by changing the amount of the sensing electric current and the direction of the sensing electric current.
In the present invention, the spin-valve type magnetoresistive thin film element may include a metallic under layer on the lower antiferromagnetic layer and a metallic protective layer on the upper antiferromagnetic layer, and the vector sum of Hbf1+Hbf2+Hd1+Hd2+Is1+Is2+S1+S2 may be adjusted to zero by creating a difference in thickness between the metallic under layer and the metallic protective layer and by changing the amount of the sensing electric current and the direction of the sensing electric current.
In the present invention, the vector sum of Hbf1+Hbf2+Hd1+Hd2+Is1+Is2+S1+S2 may be adjusted to zero by creating a difference in distance between from the center of the free magnetic layer to the lower shield layer, and from the center of the free magnetic layer to the upper shield layer, and by changing the amount of the sensing electric current and the direction of the sensing electric current.
In a conventional dual spin-valve type magnetoresistive thin film element, upper and lower laminates sandwiching a free magnetic layer are perfectly symmetrical (refer to FIG. 10). In such a structure, satisfactory asymmetry cannot be obtained, and even if satisfactory asymmetry could be obtained, the rate of resistance variation may be decreased significantly, and thus, it is not possible to improve asymmetry and the rate of resistance variation at the same time.
In the present invention, a dual spin-valve type magnetoresistive thin film element has a vertically asymmetrical structure, thus enabling satisfactory asymmetry while maintaining a high rate of resistance variation.
In the present invention, a dual spin-valve type magnetoresistive thin film element having the following film structure was fabricated, and by changing the thickness of nonmagnetic electrically-conductive layers, the relationship between the thickness of the nonmagnetic electrically-conductive layers and the rate of resistance variation was investigated. The film structure of the dual spin-valve type magnetoresistive thin film element was as follows:
Si/alumina/Ta (50)/Antiferromagnetic layer: PtMn (200)/Pinned magnetic layer (lower): Co (30)/Nonmagnetic electrically-conductive layer (lower): Cu (24)/Free magnetic layer: Co (10)+NiFe (60)+Co (10)/Nonmagnetic electrically-conductive layer (upper): Cu (24)/Pinned magnetic layer (upper): Co (30)/Antiferromagnetic layer: PtMn (200)/Ta (50)
The numeric value in parentheses represents film thickness in angstroms.
In the experiment, first, the rate of resistance variation under an external magnetic field at xc2x130 (Oe) was measured with the thickness of the upper nonmagnetic electrically-conductive layer being fixed at 24 angstroms while changing the thickness of the lower nonmagnetic electrically-conductive layer. The rate of resistance variation under an external magnetic field at xc2x130 (Oe) was also measured with the thickness of the lower nonmagnetic electrically-conductive layer being fixed at 24 angstroms while changing the thickness of the upper nonmagnetic electrically-conductive layer. The results thereof are shown in FIG. 3.
In FIG. 3, the mark ◯ shows the value when the thickness of the lower nonmagnetic electrically-conductive layer is varied with the thickness of the upper nonmagnetic electrically-conductive layer being fixed at 24 angstroms. In such a case, when the thickness of the lower nonmagnetic electrically-conductive layer is set at approximately 18 to 19 angstroms, the rate of resistance variation can be maximized, and when the thickness of the lower nonmagnetic electrically-conductive layer is set at approximately 19 angstroms or more, the rate of resistance variation is gradually decreased.
In FIG. 3, the mark xe2x97xaf shows the value when the thickness of the upper nonmagnetic electrically-conductive layer is varied with the thickness of the lower nonmagnetic electrically-conductive layer being fixed at 24 angstroms. In such a case, when the thickness of the upper nonmagnetic electrically-conductive layer is set at approximately 22 angstroms, the rate of resistance variation can be maximized, and when the thickness of the upper nonmagnetic electrically-conductive layer is set at approximately 22 angstroms or more, the rate of resistance variation is gradually decreased.
In a so-called xe2x80x9csingle spin-valve type magnetoresistive thin film elementxe2x80x9d, in which an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically-conductive layer, and a free magnetic layer, which are each one layer, are formed, the rate of resistance variation is approximately 4%. Therefore, in the present invention, the range of the thickness of the nonmagnetic electrically-conductive layer in which a rate of resistance variation of 4% or more can be obtained is set as desired. From the graph shown in FIG. 3, it is clear that when the thickness of the lower nonmagnetic electrically-conductive layer is set in the range from 16 to 38 angstroms, and when the thickness of the upper nonmagnetic electrically-conductive layer is set in the range from 19 to 38 angstroms, a rate of resistance variation of 4% or more can be obtained.
Next, in the present invention, in the dual spin-valve type magnetoresistive thin film element having the film structure described above, by changing the thickness of pinned magnetic layers, the relationship between the thickness of the pinned magnetic layers and the rate of resistance variation was investigated.
In the experiment, first, the rate of resistance variation under an external magnetic field at xc2x130 (Oe) was measured with the thickness of the upper pinned magnetic layer being fixed at 30 angstroms while changing the thickness of the lower pinned magnetic layer. The rate of resistance variation under an external magnetic field at xc2x130 (Oe) was also measured with the thickness of the lower pinned magnetic layer being fixed at 30 angstroms while changing the thickness of the upper pinned magnetic layer. The results thereof are shown in FIG. 4.
In FIG. 4, the rate of resistance variation when the thickness of the lower pinned magnetic layer only is changed, and the rate of resistance variation when the thickness of the upper pinned magnetic layer only is changed, have substantially the same curve. From FIG. 4, it is clear that a rate of resistance variation of 4% or more can be obtained by setting the thickness of the lower pinned magnetic layer and the upper pinned magnetic layer at 15 to 80 angstroms.
Next, in the present invention, experiments were carried out with respect to the relationship between the thickness of a nonmagnetic electrically-conductive layer and the interlayer coupling magnetic field Hbf which acts on a free magnetic layer from a pinned magnetic layer through the nonmagnetic electrically-conductive layer.
First, in the present invention, a single spin-valve type magnetoresistive thin film element, in which a nonmagnetic electrically-conductive layer was formed below a free magnetic layer was fabricated, and the relationship between the thickness of the nonmagnetic electrically-conductive layer and the interlayer coupling magnetic field Hbf was measured. The film structure of the single spin-valve type magnetoresistive thin film element was as follows:
Si/Alumina/Ta (50)/Antiferromagnetic layer: PtMn (200)/Pinned magnetic layer: Co (30)/Nonmagnetic electrically-conductive layer (lower): Cu (X)/Free magnetic layer: Co (20)+NiFe (60)/Ta (50)
The numeric value in parentheses represents film thickness in angstroms.
Next, a single spin-valve type magnetoresistive thin film element, in which a nonmagnetic electrically-conductive layer was formed above a free magnetic layer was fabricated, and the relationship between the thickness of the nonmagnetic electrically-conductive layer and the interlayer coupling magnetic field Hbf was measured. The film structure of the single spin-valve type magnetoresistive thin film element was as follows:
Si/Alumina/Ta (50)/Free magnetic layer : NiFe (60)+Co (20)/Nonmagnetic electrically-conductive layer (upper): Cu (X)/Pinned magnetic layer: Co (30)/Antiferromagnetic layer: PtMn (200)/Ta (50)
The numeric value in parentheses represents film thickness in angstroms.
The reason for using single spin-valve type magnetoresistive thin film elements instead of using a dual spin-valve type magnetoresistive thin film element in this experiment is that in a dual spin-valve type magnetoresistive thin film element, it is not possible to respectively measure the interlayer coupling magnetic field Hbf1 from the lower side of a free magnetic layer and the interlayer coupling magnetic field Hbf2 from the upper side of the free magnetic layer, and only the total thereof can be measured.
In FIG. 5, as shown by the mark ◯, although the interlayer coupling magnetic field is decreased as the thickness of the nonmagnetic electrically-conductive layer (lower) is increased, when the thickness of the nonmagnetic electrically-conductive layer (lower) is approximately 22 angstroms or more, the interlayer coupling magnetic field Hbf is increased, and when the thickness of the nonmagnetic electrically-conductive layer (lower) is approximately 26 angstroms or more, the interlayer coupling magnetic field Hbf is decreased again.
In FIG. 5, as shown by the mark xe2x97xaf, as the thickness of the nonmagnetic electrically-conductive layer (upper) is increased, the interlayer coupling magnetic field Hbf is steeply decreased up to a thickness of approximately 20 angstroms, and when the thickness is 20 angstroms or more, the interlayer coupling magnetic field Hbf is slowly decreased.
As described above, in the present invention, the thickness of the nonmagnetic electrically-conductive layer (lower) below the free magnetic layer is preferably set at 16 to 38 angstroms. When the thickness is in this range, as shown in FIG. 5, the intensity of the interlayer coupling magnetic field Hbf (Hbf1) is approximately in the range of from 1 to 50 (Oe).
In the present invention, the thickness of the nonmagnetic electrically-conductive layer (upper) above the free magnetic layer is preferably set at 19 to 38 angstroms. When the thickness is in this range, as shown in FIG. 5, the intensity of the interlayer coupling magnetic field Hbf (Hbf2) is approximately in the range of from 4 to 40 (Oe).
Next, in the present invention, in a dual spin-valve type magnetoresistive thin film element having the following film structure, the relationship between the thickness of pinned magnetic layers and the static magnetic coupling field from the pinned magnetic layers was sought by simulation. The film structure used was as follows:
Si/alumina/Ta (50)/Antiferromagnetic layer: PtMn (200)/Pinned magnetic layer (lower): Co (30)/Nonmagnetic electrically-conductive layer: Cu (24)/Free magnetic layer: Co (10)+NiFe (60)+Co (10)/Nonmagnetic electrically-conductive layer: Cu (24)/Pinned magnetic layer (upper): Co (30)/Antiferromagnetic layer: PtMn (200)/Ta (50)
The numeric value in parentheses represents film thickness in angstroms.
First, the static magnetic coupling field Hd (Hd1) from the lower pinned magnetic layer was sought by simulation with the thickness of the upper pinned magnetic layer being fixed at 30 angstroms while changing the thickness of the lower pinned magnetic layer. The static magnetic coupling field Hd (Hd2) from the upper pinned magnetic layer was also sought by simulation with the thickness of the lower pinned magnetic layer being fixed at 30 angstroms while changing the thickness of the upper pinned magnetic layer. The results thereof are shown in FIG. 6.
As shown in FIG. 6, when the thickness of the lower pinned magnetic layer is varied with the thickness of the upper pinned magnetic layer being fixed and when the thickness of the upper pinned magnetic layer is varied with the thickness of the lower pinned magnetic layer being fixed, in both cases, the relationship between the thickness and the static magnetic coupling field Hd is represented by the identical line, and in FIG. 6, two lines are superposed. As described above, since the upper and lower pinned magnetic layers preferably have a thickness of 15 to 80 angstroms, within this range, the static magnetic coupling fields from the upper and lower pinned magnetic layers are approximately 9 to 48 (Oe).
Based upon the experimental results described above, in the present invention, a dual spin-valve type magnetoresistive thin film element having a vertically symmetrical structure shown in FIG. 11 (comparative example) and a dual spin-valve type magnetoresistive thin film element having a vertically asymmetrical structure shown in FIG. 2 (example) were fabricated, and the intensity of the interlayer coupling magnetic field Hbf and the static magnetic coupling field Hd which influence a free magnetic layer of each dual spin-valve type magnetoresistive thin film element were obtained. In the present invention, an interlayer coupling magnetic field and a static magnetic coupling field from the lower side are defined as Hbf1 and Hd1, respectively, and an interlayer coupling magnetic field and a static magnetic coupling field from the upper side are defined as Hbf2 and Hd2, respectively.
The film structure of the vertically symmetrical dual spin-valve type magnetoresistive thin film element (comparative example) was set from the bottom as follows:
Si/alumina/Ta (50)/Antiferromagnetic layer: PtMn (200)/Pinned magnetic layer (lower): Co (40)/Nonmagnetic electrically-conductive layer (lower): Cu (22)/Free magnetic layer: Co (10)+NiFe (60)+Co (10)/Nonmagnetic electrically-conductive layer (upper): Cu (22)/Pinned magnetic layer (upper): Co (40)/Antiferromagnetic layer: PtMn (200)/Ta (50)
The numeric value in parentheses represents film thickness in angstroms. It has been confirmed by experiment that a rate of resistance variation of approximately 14.5% can be obtained in the dual spin-valve type magnetoresistive thin film element having such a film structure.
With respect to the comparative example, interlayer coupling magnetic fields Hbf1 and Hbf2 and static magnetic coupling fields Hd1 and Hd2 were obtained from the graphs shown in FIGS. 5 and 6.
In the comparative example, since the upper and lower nonmagnetic electrically-conductive layers have a thickness of 22 angstroms, as shown in FIG. 5, the interlayer coupling magnetic field Hbf1 is 2 (Oe) and the interlayer coupling magnetic field Hbf2 is 16 (Oe). In the comparative example, since the upper and lower pinned magnetic layers have a thickness of 40 angstroms, as shown in FIG. 6, the static magnetic coupling fields Hd1 and Hd2 are both 24 (Oe).
As shown in FIG. 11, since the interlayer coupling magnetic fields Hbf1 and Hbf2 and the static magnetic coupling fields Hd1 and Hd2 are applied into the free magnetic layer 1 in opposite directions, for example, when the magnetic fields in the right direction in the drawing are assumed to have positive values and the magnetic fields in the left direction in the drawing are assumed to have negative values, the interlayer coupling magnetic field Hbf1 is +2 (Oe), the interlayer coupling magnetic field Hbf2 is +16 (Oe), the static magnetic coupling field Hd1 is xe2x88x9224 (Oe), and the static magnetic coupling field Hd2 is xe2x88x9224 (Oe).
Next, the film structure of the vertically asymmetrical dual spin-valve type magnetoresistive thin film element (example) was set from the bottom as follows:
Si/alumina/Ta (50)/Antiferromagnetic layer: PtMn (200)/Pinned magnetic layer (lower): Co (40)/Nonmagnetic electrically-conductive layer (lower): Cu (18)/Free magnetic layer: Co (10)+NiFe (60)+Co (10)/Nonmagnetic electrically-conductive layer (upper): Cu (22)/Pinned magnetic layer (upper): Co (40)/Antiferromagnetic layer: PtMn (200)/Ta (50)
The numeric value in parentheses represents film thickness in angstroms. In the example, the thickness of the lower nonmagnetic electrically-conductive layer was set at 18 angstroms, the thickness of the upper nonmagnetic electrically-conductive layer was set at 22 angstroms, and laminates sandwiching the free magnetic layer was asymmetrical. It has been confirmed by experiment that a rate of resistance variation of approximately 16.5% can be obtained in the dual spin-valve type magnetoresistive thin film element having such a film structure.
With respect to the example, interlayer coupling magnetic fields Hbf1 and Hbf2 and static magnetic coupling fields Hd1 and Hd2 were obtained from the graphs shown in FIGS. 5 and 6.
In the example, since the lower nonmagnetic electrically-conductive layer has a thickness of 18 angstroms, as shown in FIG. 5, the interlayer coupling magnetic field Hbf1 is 20 (Oe), and since the upper nonmagnetic electrically-conductive layer has a thickness of 22 angstroms, the interlayer coupling magnetic field Hbf2 is 16 (Oe).
In the example, since the upper and lower pinned magnetic layers have a thickness of 40 angstroms, as shown in FIG. 6, the static magnetic coupling fields Hd1 and Hd2 are both 24 (Oe).
In this example, since the interlayer coupling magnetic fields Hbf1 and Hbf2 and the static magnetic coupling fields Hd1 and Hd2 are also applied into the free magnetic layer 1 in opposite directions (refer to FIG. 2), if the interlayer coupling magnetic fields Hbf1 and Hbf2 are assumed to have positive values, the static magnetic coupling fields Hd1 and Hd2 have negative values. Therefore, the interlayer coupling magnetic field Hbf1 is +20 (Oe), the interlayer coupling magnetic field Hbf2 is +16 (Oe), the static magnetic coupling field Hd1 is xe2x88x9224 (Oe), and the static magnetic coupling field Hd2 is xe2x88x9224 (Oe).
The values of interlayer coupling magnetic fields Hbf1 and Hbf2 and static magnetic coupling fields Hd1 and Hd2 in the comparative example (vertically symmetrical dual spin-valve type magnetoresistive thin film element) and the example (vertically asymmetrical dual spin-valve type magnetoresistive thin film element) are shown in Table 1.
In the far-right column in Table 1, the total of interlayer coupling magnetic fields Hbf1 and Hbf2 and static magnetic coupling fields Hd1 and Hd2 is shown. In the comparative example, the total is xe2x88x9230 (Oe), and in the example, the total is xe2x88x9212 (Oe). That is, in the dual spin-valve type magnetoresistive thin film element of the comparative example, a magnetic field of xe2x88x9230 (Oe) influences the free magnetic layer, and in the dual spin-valve type magnetoresistive thin film element of the example, a magnetic field of xe2x88x9212 (Oe) influences the free magnetic layer. As is evident from the above, in the example, the influence of a magnetic field acting on the free magnetic layer is reduced in comparison with the comparative example.
In the vertically symmetrical dual spin-valve type magnetoresistive thin film element, as shown in FIG. 11, induction magnetic fields by the sensing electric current 9 influence the free magnetic layer 1 as Is1 from the lower side of the free magnetic layer 1 and influence the free magnetic layer 1 as Is2 from the upper side of the free magnetic layer 1. However, in the vertically symmetrical structure, since the induction magnetic fields Is1 and Is2 have the same intensity and are applied into the free magnetic layer 1 in opposite directions, the induction magnetic fields Is1 and Is2 are offset with respect to each other, and thus the free magnetic layer 1 is not influenced by the induction magnetic fields.
Therefore, in the vertically symmetrical dual spin-valve type magnetoresistive thin film element, in order to adjust asymmetry to 0%, there is a possibility for asymmetry to be set at 0% by a shield bias magnetic field, i.e., the shield bias magnetic field S1 (vector)+the shield bias magnetic field S2 (vector). That is, in FIG. 11, by making the distance GL1 from the center of the free magnetic layer 1 to the lower shield layer 10 different from the distance GL2 from the center of the free magnetic layer 1 to the upper shield layer 11, the shield bias magnetic fields S1 and S2 applied to the free magnetic layer 1 have different intensities.
An experiment was carried out with respect to the relationship between the sensing electric current and asymmetry by setting the distances GL1 and GL2 at different values in the vertically symmetrical dual spin-valve type magnetoresistive thin film element shown as the comparative example. The experimental results are shown in FIG. 7. With respect to the sensing electric current in the horizontal axis, when the sensing electric current 9 shown in FIG. 11 flows perpendicularly with respect to the drawing toward the front, the sensing electric current is assumed to have a positive value, and when the sensing electric current 9 flows perpendicularly with respect to the drawing toward the back, the sensing electric current is assumed to have a negative value.
First, when the distances GL1 and GL2 are set at 1,050 angstroms, as shown by the mark xe2x96xa1 in FIG. 7, even if the sensing electric current is changed, asymmetry remains at a certain value, and it is not possible to improve an asymmetry of approximately xe2x88x9220%.
Next, when the distance GL1 is set at 1,400 angstroms and the distance GL2 is set at 700 angstroms, as shown by the mark xe2x97xaf in FIG. 7, asymmetry may be varied by applying the sensing electric current, and asymmetry can be adjusted to 0% when the sensing electric current is applied at approximately 6 mA.
Next, when the distance GL1 is set at 700 angstroms and the distance GL2 is set at 1,400 angstroms, as shown by the mark ◯ in FIG. 7, asymmetry may be varied by applying the sensing electric current, and asymmetry can be adjusted to 0% when the sensing electric current is applied at approximately xe2x88x926 mA.
As described above, in the vertically symmetrical dual spin-valve type magnetoresistive thin film element, by making the distance GL1 different from the distance GL2, and by changing the intensity and direction of the sensing electric current, the intensities and directions of the shield bias magnetic fields S1 and S2 can be changed, and thus asymmetry can be adjusted to 0%.
In contrast, in the vertically asymmetrical dual spin-valve type magnetoresistive thin film element, asymmetry can be adjusted to 0% either by setting the distances GL1 and GL2 at different values, or by setting the distances GL1 and GL2 at the same value.
When a spin-valve type magnetoresistive thin film element has a vertically asymmetrical structure, the intensity of a sensing electric current flowing through the layers above a free magnetic layer differs from that of a sensing current flowing through the layers below the free magnetic layer, and there is a difference in intensity between induction magnetic fields Is1 and Is2 by the sensing electric current. Thus, the induction magnetic fields Is1 and Is2 are not offset with respect to each other, and an induction magnetic field determined by the vector sum of the induction magnetic field Is1 and the induction magnetic field Is2 can be used for adjusting asymmetry to 0%. In the dual spin-valve type magnetoresistive thin film element of the example, since the upper nonmagnetic electrically-conductive layer has a larger thickness than that of the lower nonmagnetic electrically-conductive layer, a larger amount of the sensing electric current flows through the layers above the free magnetic layer in comparison with the layers below the free magnetic layer.
An experiment was carried out with respect to the relationship between the sensing electric current and asymmetry by setting the distance GL1 from the center of the free magnetic layer 20 to the shield layer 30, and the distance GL2 from the center of the free magnetic layer 20 to the shield layer 31, at different values in the vertically asymmetrical dual spin-valve type magnetoresistive thin film element (example) shown in FIG. 2. The experimental results are shown in FIG. 8. With respect to the sensing electric current in the horizontal axis shown in FIG. 8, when the sensing electric current shown in FIG. 2 flows perpendicularly with respect to the drawing toward the front, the sensing electric current is assumed to have a positive value, and when the sensing electric current flows perpendicularly with respect to the drawing toward the back, the sensing electric current is assumed to have a negative value.
In FIG. 8, the experimental results for the vertically symmetrical dual spin-valve type magnetoresistive thin film element (comparative example) are also shown, in which the distances GL1 and GL2 are both set at 1,050 angstroms.
As shown in FIG. 8, in the vertically asymmetrical dual spin-valve type magnetoresistive thin film element (example), when the distance GL1 is set at 1,400 angstroms and the distance GL2 is set at 700 angstroms, asymmetry can be adjusted to 0% when the sensing electric current is applied at approximately 4 mA.
When the distance GL1 is set at 700 angstroms and the distance GL2 is set at 1,400 angstroms, asymmetry can be adjusted to 0% when the sensing electric current is applied at approximately at xe2x88x924 mA.
As described above, both in the vertically symmetrical dual spin-valve type magnetoresistive thin film element and in the vertically asymmetrical duel spin-valve type magnetoresistive thin film element, asymmetry can be adjusted to 0% by making the distance between the center of the free magnetic layer and the upper shield layer different from the distance between the center of the free magnetic layer and the lower shield layer. However, there is a difference in the amount of the sensing electric current required for adjusting asymmetry to 0% between the vertically symmetrical structure and the vertically asymmetrical structure.
As described above, in the vertically symmetrical dual spin-valve type magnetoresistive thin film element as the comparative example, as shown in FIG. 7, when GL1 is set at 1,400 angstroms and GL2 is set at 700 angstroms, a sensing electric current of 6 mA is required to adjust asymmetry to 0%.
On the other hand, in the vertically asymmetrical dual spin-valve type magnetoresistive thin film element as the example, as shown in FIG. 8, when GL1 is set at 1,400 angstroms and GL2 is set at 700 angstroms, a sensing current of 4 mA is required to adjust asymmetry to 0%.
Consequently, in the vertically symmetrical dual spin-valve type magnetoresistive thin film element (comparative example), a sensing electric current which is larger by 2 mA must be applied to adjust asymmetry to 0% in comparison with the vertically asymmetrical dual spin-valve type magnetoresistive thin film element (example). The difference of 2 mA in sensing electric current may vary with the thickness of the individual layers constituting dual spin-valve type magnetoresistive thin film elements. As shown in Table 1, in the comparative example, the total of interlayer coupling magnetic fields Hbf1 and Hbf2 and static magnetic coupling fields Hd1 and Hd2 is xe2x88x9230 (Oe), and in contrast, in the example, the total of interlayer coupling magnetic fields Hbf1 and Hbf2 and static magnetic coupling fields Hd1 and Hd2 is xe2x88x9212 (Oe). In the example, the absolute value of the magnetic field to be compensated for by the shield bias magnetic field is originally smaller, and in the example, since the induction magnetic field by the sensing electric current (vector sum of the induction magnetic field Is1 and the induction magnetic field Is2) is also taken into account, asymmetry can be adjusted to 0% by the shield bias magnetic field (vector sum of the shield bias magnetic field S1 and the shield bias magnetic field S2) and by the induction magnetic field by the sensing electric current. Both the intensity of the shield bias magnetic field and the intensity of the induction magnetic field by the sensing electric current depend on the amount of the sensing electric current. By properly adjusting the distances GL1 and GL2 and the direction of the sensing electric current, the shield bias magnetic field and the induction magnetic field by the sensing electric current, which are applied to the free magnetic layer, can be set in the same direction. If the shield bias magnetic field and the induction magnetic field by the sensing electric current are set in the same direction, the required strength of the magnetic field can be compensated for both by the shield bias magnetic field and by the induction magnetic field by the sensing electric current, with a smaller amount of sensing electric current, in comparison with the amount of sensing electric current required in the vertically symmetrical dual spin-valve type magnetoresistive thin film element (comparative example) in which asymmetry can be adjusted to 0% by the shield bias magnetic field alone.
Of course, the present invention covers both a vertically symmetrical dual spin-valve type magnetoresistive thin film element in which the distances GL1 and GL2 are different and a vertically asymmetrical dual spin-valve type magnetoresistive thin film element in which the distances GL1 and GL2 are different.
Next, in order to adjust asymmetry to 0% only by induction magnetic fields without using shield bias magnetic fields, an experiment was carried out with respect to the relationship between the sensing electric current and asymmetry, by setting the distances GL1 and GL2 at 1,050 angstroms. The experimental results are shown in FIG. 9. With respect to the sensing electric current in the horizontal axis shown in FIG. 9, when the sensing electric current shown in FIG. 2 flows perpendicularly with respect to the drawing toward the front, the sensing electric current is assumed to have a positive value, and when the sensing electric current flows perpendicularly with respect to the drawing toward the back, the sensing electric current is assumed to have a negative value.
In FIG. 9, the experimental results for the vertically symmetrical dual spin-valve type magnetoresistive thin film element (comparative example) are also shown, in which the distances GL1 and GL2 are both set at 1,050 angstroms. As shown in FIG. 9, in the comparative example, even if the sensing electric current is changed, asymmetry remains a certain value, which is approximately xe2x88x9220%.
In the vertically asymmetrical dual spin-valve type magnetoresistive thin film element, the relationship between the sensing electric current and asymmetry was measured with the distances GL1 and GL2 being set at 1,050 angstroms.
As shown in FIG. 9, as the sensing electric current is changed, asymmetry varies, and when the sensing electric current is applied at approximately 10 mA, asymmetry can be adjusted to 0%. In the vertically asymmetrical dual spin-valve type magnetoresistive thin film element having the film structure described above, since the thickness of the upper nonmagnetic electrically-conductive layer is greater than that of the lower nonmagnetic electrically-conductive layer by 4 angstroms, a larger amount of sensing electric current flows in the upper side than in the lower side of the free magnetic layer.
If the amount of sensing electric current is increased, the induction magnetic field Is2 generated in the upper side of the free magnetic layer 20 is increased in comparison with the induction magnetic field Is1 generated in the lower side of the free magnetic layer 20. It is easily understood also from FIG. 9 that the induction magnetic field determined by the vector sum of the induction magnetic field Is1 and the induction magnetic field Is2 is proportional to the sensing electric current intensity.
Therefore, in the vertically asymmetrical dual spin-valve type magnetoresistive thin film element, if the direction of the sensing electric current and the sensing electric current intensity are properly adjusted, even without using shield bias magnetic fields, asymmetry can be adjusted to 0% without fail.
As described above, in the present invention, by actively fabricating a dual spin-valve type magnetoresistive thin film element with a vertically asymmetrical structure, and by properly adjusting the direction of the sensing electric current and the intensity thereof, all the magnetic fields influencing the free magnetic layer can be cancelled, and thus asymmetry can be adjusted to 0%.
In the example described above, although the upper and lower nonmagnetic electrically-conductive layers are formed at different thickness to construct the vertically asymmetrical structure, any pair of identical layers sandwiching the free magnetic layer may be formed at different thickness to obtain the vertically asymmetrical structure.
In the present invention, in order to construct the vertically asymmetrical structure, the thickness of the upper pinned magnetic layer may be different from that of the lower pinned magnetic layer, the thickness of the upper antiferromagnetic layer may be different from that of the lower antiferromagnetic layer, or the thickness of a metallic under layer formed on the lower antiferromagnetic layer may be different from that of a metallic protective layer formed on the upper antiferromagnetic layer.
Instead of forming one pair of identical layers sandwiching the free magnetic layer at different thickness, two or more pairs of identical layers may be formed at different thickness to construct the vertically asymmetrical structure.
Additionally, even in a vertically symmetrical dual spin-valve type magnetoresistive thin film element, by setting the distance between the center of a free magnetic layer and an upper shield layer at a different value from that of the distance between the center of the free magnetic layer and a lower shield layer, a shield bias magnetic field can be used, and thus asymmetry can be adjusted to 0%.
Even in the vertically symmetrical dual spin-valve type magnetoresistive thin film element as shown in FIG. 11, in which the distance GL1 is the same as the distance GL2, by properly setting the thickness of the individual layers constituting the dual spin-valve type magnetoresistive thin film element, asymmetry can be adjusted to 0%. For example, the film structure may be set from the bottom as follows:
Si/alumina/Ta (50)/Antiferromagnetic layer: PtMn (200)/Pinned magnetic layer (lower): Co (20)/Nonmagnetic electrically-conductive layer (lower): Cu (20)/Free magnetic layer: Co (10)+NiFe (60)+Co (10)/Nonmagnetic electrically-conductive layer (upper): Cu (20)/Pinned magnetic layer (upper): Co (20)/Antiferromagnetic layer: PtMn (200)/Ta (50)
The numeric value in parentheses represents film thickness in angstroms. In the above film structure, with reference to FIGS. 5 and 6, it is known that the interlayer coupling magnetic field Hbf1 is 3 (Oe), the static magnetic coupling field Hd1 is xe2x88x9212 (Oe), the interlayer coupling magnetic field Hbf2 is 22 (Oe), and the static magnetic coupling field Hd2 is xe2x88x9212 (Oe), thus making the total approximately zero. However, in such a film structure, although satisfactory asymmetry is obtained, since the upper and lower pinned magnetic layers have a small thickness of 20 angstroms, the rate of resistance variation is decreased to 7.0% (refer to FIG. 3).
Satisfactory asymmetry may also be obtained in a film structure as follows:
Si/alumina/Ta (50)/Antiferromagnetic layer: PtMn (200)/Pinned magnetic layer (lower): Co (40)/Nonmagnetic electrically-conductive layer (lower): Cu (19)/Free magnetic layer: Co (10)+NiFe (60)+Co (10)/Nonmagnetic electrically-conductive layer (upper): Cu (19)/Pinned magnetic layer (upper): Co (40)/Antiferromagnetic layer: PtMn (200)/Ta (50)
The numeric value in parentheses represents a film thickness in angstroms. In the above film structure, with reference to FIGS. 5 and 6, it is known that the interlayer coupling magnetic field Hbf1 is 10 (Oe), the static magnetic coupling field Hd1 is xe2x88x9224 (Oe), the interlayer coupling magnetic field Hbf2 is 40 (Oe), and the static magnetic coupling field Hd2 is xe2x88x9224 (Oe), thus making the total approximately zero. However, in such a film structure, although satisfactory asymmetry is obtained, since the upper and lower nonmagnetic electrically-conductive layers have a small thickness of 19 angstroms, the rate of resistance variation obtained will be 10.1%, which is not very high for a dual spin-valve type magnetoresistive thin film element (refer to FIG. 4).
That is, an object of the present invention is to adjust asymmetry to 0% while maintaining a high rate of resistance variation, which is the major characteristic of dual spin-valve type magnetoresistive thin film elements. Therefore, first, a vertically asymmetrical structure is fabricated by selecting the thickness of the individual layers so as to obtain a high rate of resistance variation, and thus induction magnetic fields by a sensing electric current, that could not be used conventionally, can be actively used, enabling the adjustment of asymmetry to 0%.